The present invention relates to an ultrasonic wave nebulizer which atomizes water or liquid with small power consumption, in particular, relates to such a nebulizer which operates with low temperature, and may adjust to the size of mist easily.
Conventionally, an ultrasonic wave nebulizer for atomizing water to adjust room humidity has been known. In that atomizer, an ultrasonic wave vibrator which vibrates in thickness direction is mounted at a bottom of a water tank. FIG. 1A shows a prior atomizer in which a tank 102 which has an ultrasonic wave vibrator 103 at the bottom of the same contains water 101. When the piezoelectric vibrator 103 vibrates a water column 104 is generated on surface of water 101, and the water column 104 generates fine mist.
FIG. 1B shows the relationship between water depth (H) and amount of generated mist (vertical axis). When the vibration frequency is 1.7 MHz, and the diameter of the vibrator is 20 mm, the maximum generation of mist is obtained when the water depth is from H=30 mm to H=40 mm.
However, the prior atomizer has the disadvantage that the size of the device is rather large, since the vibrator must be mounted at the bottom of the water tank with the depth of 30-40 mm.
Further, the prior atomizer has the disadvantage that the power consumption is rather large as shown in FIG. 1C in which the horizontal axis shows the power consumption, and the vertical axis shows the amount of the mist. The minimum power consumption W.sub.0 in a prior art is around 6 watts. As an atomizer for converting 400 cc/hour cm.sup.3 /hour) of water to mist consumes about 40 watts, that power consumption is too high for a battery operating atomizer or a portable atomizer.
Another prior atomizer is shown in JP UM second publication 38950/88, which has a cone shaped horn having a resonator plate on one end having a small diameter, and a piezoelectric vibrator on the other end having a large diameter. Water is supplied on the resonator plate. The spacing between the resonator plate and the vibrator is designed to be half wavelength. As the vibration of the vibrator is amplified according to the ratio of the area of the plate to the area of the vibrator, the amplitude of the plate is very large, and water drop on the plate is atomized.
However, the atomizer shown in JP UM 38950/88 has the disadvantages that (1) the essential operation area of the plate for atomizing is small, (2) as the vibration is mechanically amplified, the horn must be manufactured very precisely, and a problem could occur due to the difference of the thermal expansion between the vibrator and the horn, and (3) the size of mist is rather large for instance 20 .mu.m), as the operation frequency must be rather low (100-150 KHz for instance) because of the mechanical amplification.
In order to solve the above disadvantages, we have proposed an improved nebulizer in U.S. Ser. No. 07/889067, and EP 420177.5, which shows a nebulizer having a disc-shaped piezoelectric vibrator, and a mesh located close to the vibrator so that thin water film is provided between the mesh and the vibrator. Upon excitation of the vibrator with high frequency, which is almost the same as the resonant frequency of the vibrator, the water film is converted to mist.
The present invention is an improvement on said previously filed nebulizer. The improvements reside in that the operation temperature of a vibrator is decreased, and that the size of generated mist is easily adjustable.
When the temperature is high, the nebulizer cannot be used for atomizing liquid which dissolves at high temperature. Further, the size of mist in the prior art is not easily adjusted, although the size of mist depends upon the exciting frequency of a piezoelectric vibrator, since the exciting frequency must coincide with the resonant frequency of a piezoelectric vibrator.